The embodiments described in this disclosure will generally be discussed in relation to deployment of stent grafts into the aorta, but this disclosure is not so limited and can be applied to other vasculature or other body lumens.
Prostheses such as stents or stent grafts may be inserted into an anatomical vessel or duct for various purposes. Stents may maintain or restore patency in a formerly blocked or constricted passageway, for example, following a balloon angioplasty procedure. Other stents may be used for different procedures. For example, stents placed in or about a graft have been used to hold the graft in an open configuration to treat an aneurysm. Additionally, stents coupled to one or both ends of a graft may extend proximally or distally away from the graft to engage a healthy portion of a vessel wall away from a diseased portion of an aneurysm to provide endovascular graft fixation.
Stents may be either self-expanding or balloon-expandable. Stents also can have characteristics of both self-expanding and balloon-expandable stents. Self-expanding stents may be delivered to a target site in a compressed configuration and subsequently expanded by removing a delivery sheath, removing trigger wires, and/or releasing diameter reducing ties. A self-expanding stent may expand primarily based on its own expansive force without the need for further mechanical expansion. A stent may be made of a shape-memory alloy such as nitinol to cause the stent to return to a predetermined configuration upon removal of the sheath or other device maintaining the stent in its predeployment compressed configuration.
When trigger wires are used as a deployment control mechanism, the trigger wires may releasably couple the proximal and/or distal ends of a stent or stent graft to a delivery catheter. Typically, one or more trigger wires are looped through a portion of the stent near a vertex of the stent. For example, trigger wires may be used to restrain a “Z-stent” or Gianturco stent comprising a series of substantially straight segments interconnected by a series of bent segments. The trigger wires may be disposed through, and pull upon, the bent segments to pull the stent closely against the delivery catheter.
Trigger wires also may be used in conjunction with different stent designs such as cannula-cut stents having relatively acute or pointed bends. The designs of cannula-cut stents may facilitate compression of the stent to a relatively small delivery profile due to the tight bends of the apices. With such stents, the trigger wires may be looped around one or more vertices corresponding to the proximal and/or distal apices, e.g., a location where an individual apex splits into two separate strut segments.
Releasing the trigger wires will release the stent from the delivery catheter to allow the stent to expand. Multiple trigger wires generally may be released simultaneously. Depending, for example, on the number of trigger wires and the radial expansion force exerted by the stent, releasing the trigger wires may require a relatively great amount of force. Additionally, upon releasing the trigger wires, the stent may expand relatively quickly causing undesirable movement of the stent within a vessel.
In view of the above, it would be desirable to provide a delivery system requiring a reduced amount of force for releasing the trigger wires. It would also be desirable to provide a delivery system capable of releasing a stent in stages to better control the placement of the stent within a vessel.